OZONE EFFECTS ON THE BIOMASS, NODULATION AND NITROGENASE ACTIVITY OF CLOVER CULTIVARS

1,2HEWITT., D., 1MILLS, G., 1HAYES, F., 2WILKINSON, S. & 2DAVIES, W.

1 CENTRE FOR ECOLOGY AND HYDROLOGY 2 LANCASTER UNIVERSITY

How do you make a cow? Amongst other things, 1kg of beef needs roughly: • 460 L drinking water • 43kg grain/hay • 46,000 L water to make the feed • 25g of N per kg of meat • 700kg cow ~ 17.5kg N This N must be obtained from the pasture forage

?+?= GOOGLE Images 2013

A temperate pasture may require >100kg/ha-1 yr-1 of N input to meet the demands of grazing livestock.

• Some will be deposited (UK total N deposits <10kg - >21kg/ha yr-1) • Applied in fertilisers

• Obtained via clover (Trifolium spp.)

ROTAP, 2011

GOOGLE Images 2013

• Bare symbioses with N-fixing rhizobia in organs called root nodules in N-limited conditions.

• Legumes are the primary source of protein for a substantial proportion of human population.

• Importance of legumes in agriculture known for millennia

White clover root nodules

Clovers are legumes (Fabaceae)

• Ground level ozone most damaging air pollutant • Causes multi-billion $ losses annually in a range of important arable crops. • Further increases predicted during cause of this century

The Royal Society, 2008

GOOGLE Images 2013

Ozone concentrations have increased since pre-industrial era

• Numerous studies show ozone may affect reductions in composition yield, & forage quality in temperate pasture

• Ozone shown to reduce nodulation/fixation in number of legumes • Modern cultivars of clover

Ozone effects on pasture

Solardome study • Studies based at the CEH solardome facility (nr Bangor)

• Test of modern clover cultivars recommended for general use in grazed pasture (British Grassland Society, 2012).

• White clover (Trifolium repens cv. Crusader) • Red Clover (Trifolium pratense cv. Merviot)

Crusader Merviot

At start of experiment

Broad aim to quantify physiological impacts on the cultivars.

• Plants exposed in to 7 ozone scenarios (with a unique scenario per dome).

• Scenarios based on a profile recorded at Aston Hill monitoring station (Flintshire, UK).

• 6 replicates per scenario; exposed for 12 weeks

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R² = 0.87 P<0.001

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R2 = 0.2108 P=0.09

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Ozone injury

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● = Merviot ○ = Crusader

Ozone injury and stomatal conductance (gs)

Shoot biomass Root biomass Root:shoot

Shoot and Root biomass

● = Merviot ○ = Crusader

Nodules per pot Mass per nodule Nodule mass per pot

Nodule biomass

● = Merviot ○ = Crusader

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Nodules 0.7->1.5mm

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Nodule size

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In-situ nitrogenase activity (Acetylene reduction assays)

Low ozone High ozone

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Week 11

P<0.1

P<0.05

What does this mean for the UK? Using 10 x 10km grid square and AOT40 values for pasture-growing areas of the UK*,

in a high ozone year (2006), there was potentially : April – June : a mean 12% reduction in nodule mass July – September: a mean 8% reduction in nodule mass

April-June July-Sept

* Data from Mhairi Coyle, in Mills et al., 2011, O3 and food security in the UK report for Defra

Summary and conclusions

• Systemic reductions in below ground biomass and nodulation, and reduction in nitrogenase activity.

• Perhaps arising from a reduction in the translocation of assimilate.

• Continuing increases in the level of ozone may cause lasting declines in pasture fertility and productivity.

• Mixed community of high sugar Ryegrass (‘AberMagic’) and Crusader

• 6 O3 treatments +/-Intermittent drought

• Sequential harvests and nitrogen fixation assays (= 220 pots!).

• Paper close to submission

This growing season……

Special thanks to Aled Williams, Anni Gibeif, Steve Hughes, Harry Harmens, Chris Evans, Peter Wieland, Vicent Calatayud, Serena Wagg and Chiara Premoli for their advice and assistance. This is a NERC funded project (project code: NEC04456).

Acknowledgements

Thanks for your time!

R² = 0.54 P=0.07

R² = 0.99 P=0.01

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